(1) Field of the Invention
The present invention relates to a powdery adhesive and a process for the preparation thereof. The powdery adhesive of the present invention is preferably used as a spot adhesive for bonding two substrates of an electro-optical element comprising a liquid crystal, such as a smectic liquid crystal or a nematic liquid crystal, which is supported between the substrates, especially two substrates having a uniform spacing of an order of .mu.m.
(2) Description of the Related Art
A liquid crystal electro-optical element comprises two substrates confronting each other with a certain spacing therebetween and a liquid crystal sealed in the spacing, in which each substrate comprises a driving transparent electrode film and an orienting film for orienting liquid crystal molecules, which are formed on the surface of a glass sheet.
A liquid crystal electro-optical element comprising a ferroelectric liquid crystal showing the chiral smectic C phase was recently developed (see, for example, Japanese Unexamined Patent Publication No. 56-107216). A liquid crystal substance having the chiral smectic C phase, such as p-decyloxybenzylidene-p'-amino-2-methylbutyl cinnamate or p-hexyloxyben-zylidene-p'-amino-2-chloropropyl cinnamate, has a structure in which liquid crystal molecules are spirally oriented. If the liquid crystal is injected between two substrates arranged to confront each other with a spacing narrower than the frequency of this spiral, the liquid crystal molecules lose the spiral structure, and simultaneously, a bistable state characteristic is produced by the influence of the orienting film. Two stable states are alternated at a high speed in response to an applied voltage by utilizing the ferroelectric property possessed by the liquid crystal molecules, whereby the liquid crystal is driven. If the voltage is removed, the liquid crystal molecules maintain one of the two stable states, and therefore, the liquid crystal has a memory property.
However, since the liquid crystal has the chiral smectic C phase, to realize the bistable state in the liquid crystal substance, two substrates must be arranged with a certain spacing smaller than several .mu.m, but since distortions and warping are present in the substrates, it is difficult to uniformly decrease the spacing between the substrates.
Under this background, it is desirable to provide a technique of forming a cell structure in which two substrates are arranged in parallel with as narrow a spacing as possible therebetween.
It is also desirable to provide a technique of producing a stability against shock or movements of the liquid crystal in a liquid crystal electro-optical element.
A liquid electro-optical element is sometimes exposed to a low temperature during transportation or use, and the liquid crystal electro-optical element generally must have be stable at about -30.degree. C. and drivable at about -20.degree. C. Among the members constituting the liquid crystal electro-optical element, the glass, spacer particles or adhesive particles have a linear expansion coefficient on an order of 10.sup.-5 /.degree.C., but the linear expansion coefficient of the liquid crystal is on an order of 10.sup.-3 /.degree.C. Accordingly, as the element is cooled from a temperature close to room temperature to a lower temperature, the liquid crystal is unilaterally shrunk. Accordingly, by a simple calculation, it will be readily understood that, if the temperature is lowered by about 50.degree. C. from room temperature to -30.degree. C., in about 15% of the display area, the state in which the liquid crystal is not filled, i.e., the state wherein vacuum bubbles occur, is formed, and a blank portion is formed in the display picture. Practically, because of distortions of the substrates and the deformation of spacer particles and adhesive particles, the quantity of vacuum bubbles is smaller than the calculated quantity, but it is apparent that vacuum bubbles are formed, and thus the quality of the liquid crystal electro-optical element is drastically degraded at low temperatures.